Method of performing an area update for a terminal equipment in a communication network

ABSTRACT

The present invention proposes a method of performing an area update for a terminal equipment ( 4 A,  4 B) in a communication network ( 1, 2, 3, 5, 6 ), the communication network comprising at least two areas ( 5, 6 ) being defined within an access network, at least one of said areas being served by at least two core network elements ( 1 - 2, 2 - 3 ) of corresponding network element types, each of said at least two core network elements communicating with said access network defining said areas via a different interface (Iu, Gb), the method comprising the steps of: monitoring, at the terminal equipment side, via which of said at least two core network elements ( 1, 2 ) serving a currently visited area ( 5 ) the communication with the terminal equipment ( 4 A) is effected, detecting, at the terminal equipment side, an area update condition for said terminal ( 4 A,  4 B), requesting, by said terminal equipment, an area update for said terminal equipment ( 4 B), and wherein said terminal equipment ( 4 B) sets an identifier in said area update request identifying the core network element via which the communication with the terminal equipment ( 4 A) has previously been effected. Still further, the present invention proposes also an accordingly adapted terminal equipment.

TITLE OF THE INVENTION

[0001] A method of performing an area update for a terminal equipment ina communication network

FIELD OF THE INVENTION

[0002] The present invention relates to method of performing an areaupdate for a terminal equipment in a communication network, and also toa correspondingly adapted terminal equipment.

BACKGROUND OF THE INVENTION

[0003] Generally, communication networks consist of an access networkand a core network. The access network is specifically adapted to aconnection technology used for terminal equipment communicating with/viathe network, whereas the core network is connection technologyindependent and manages the functions the network offers to theterminals registered in the network.

[0004] Currently, for example, there exists the GSM network (GSM=GlobalStandard for Mobile Communication), consisting of a so called basestation subsystem BSS as the access network part and the core networkcomprising e.g. the mobile services switching center MSC, a homelocation register HLR, visitor location register VLR etc. The basestation subsystem BSS is connected to the core network via an interfaceknown as A-interface. Further, the base station subsystem comprises aplurality of base station BS and/or base transceiver stations BTS undercontrol of a base station controller BSC. Each base station BS defines acell and a plurality of cells form a location area. Typically, alocation area has a size (number of cells) such that one MSC may effectcontrol of communication within a location area. The above brieflydescribed GSM communication system is also known as a second generationsystem (2G), which initially was basically intended and provisioned forspeech data transmission (circuit switched data, real time datatransmission).

[0005] Meanwhile, however, the need for packet data transmission (datadifferent from speech) (non-real time, packet switched data) hasincreased, which led to the development of a so-called GPRS network(General Packet Radio Service). The GSM and GPRS communication networkexist somewhat in parallel and rely on substantially the same accessnetwork. With regard to the core network, in a GPRS network the functionof the MSC is performed by so-called GPRS Support Nodes GSN, among whichthere are Serving GPRS support nodes SGSN (and gateway GPRS supportnodes GGSN). The BSS is connected to the SGSN via an interface known asGb interface.

[0006] Hence, a single cell in such a communication network scenario maybe connected to different core network elements of different types, i.e.SGSN and/or MSC/VLR.

[0007] Now, in case a terminal equipment (e.g. mobile station MS) hasmoved within the network such that a new MSC/VLR and/or new SGSN is incharge for controlling communication in that part of the network, thenecessity for a routing and/or location area update arises. The terminalthen performs a routing and/or location area update, i.e. requests a newSGSN and/or MSC/VLR to take over communication control for therequesting terminal equipment. In such a routing and/or location areaupdate RAU/LAU, the terminal equipment transmits the old, i.e. previous,routing area identity RAI and/or location area identity LAI of therouting/location area it was previous attached to and/or communicatingwith.

[0008] Using the transmitted RAI (LAI), the new core network elementfinds an address of the core network element previously in charge forcontrolling/managing communication with the terminal, i.e. the new corenetwork element in the new routing area may locate the previous (old)core network element (SGSN and/or MSC/VLR) from where the subscriberdata for the requesting terminal equipment are sent to the core networkelement at the new (current) location (new SGSN and/or new MSC/VLR).

[0009] With a continuously progressing development in communicationnetworks, also a so-called third generation (3GPP=3^(rd) generationpartnership project) of communication networks is being developed. Thecommunication network of the third generation is also referred to asUMTS (Universal Mobile Telecommunication System). According to UMTS/3GPPspecifications, base stations in GSM correspond to Node_B's, mobilestations MS as terminal equipment are referred to as user equipment UE,etc. Also with a third generation (3G) communication network, a circuitswitched data transfer (e.g. for speech) as well as a packet switcheddata transfer is enabled. To this end, the 3G access network isconnected or at least connectable via a Iu-CS interface to a 3G MSC/VLRand via a Iu-PS interface to a 3G SGSN.

[0010] With a demand that most recently developed equipment should bedownward compatible, i.e. compatible to previously developedstandardized systems, there will arise a situation, in which, forexample, a 2G SGSN as well as a 3G SGSN are both connected to the samecell and/or location (routing) area of an access network.

[0011] For example, so-called GERAN cells enable the connection of 2G aswell as of 3G core network elements (e.g. 2G SGSN and 3G SGSN) to thesame cell/location (routing) area. (GERAN=GSM EDGE Radio Access Network,EDGE=Enhanced Data rates for GSM Evolution). In case of SGSN's as anexample for core network elements, a 2G SGSN is connected to a GERANcell/routing area (i.e. to the GERAN access network) via the Gbinterface, whereas a 3G SGSN is connected thereto via the Iu-PSinterface. Such a connection to a single GERAN cell/routing area ofdifferent core network elements of the same type (i.e. SGSN with Iu-PSor Gb interface), is, however, required in 3G communication networks.

[0012] However, because a single routing area (or cell (as a smallestconceivable routing area)) can be connected to two different SGSN's, onewith Iu and other with Gb interface, the new SGSN receiving the terminalequipment's routing area update (RAU) request upon the detection of anecessity for routing area update does not know from which SGSN itshould request the subscriber information associated with the requestingterminal, because the old routing area identifier RAI identifying therouting area in which the terminal equipment was previously present mayindicate two different core network elements (i.e. 2G SGSN and 3G SGSN).

[0013] If, however, in the chosen example, a new SGSN does not knowwhich previous SGSN to contact to retrieve the subscriber information ofthe requesting terminal equipment, a routing area update for a terminalequipment may fail and a call may be dropped.

[0014] Previously, in order to solve such a problem, it has beenproposed to assign two separate routing area identities (RAI) to eachrouting area (and/or cell). However, assigning two identities inevitablydoubles the address space for the routing areas, which is undesirable interms of an additional need of network management in the core and accessnetwork. Also, the respective access network RAN (more specifically, thebase stations and/or Node_B's) will have to broadcast two routing areaidentities for each routing area, while also terminals listening to thebroadcasted information will have to be adapted to properly processand/or interpret the two broadcasted identities per routing area.

[0015] Thus, this previously proposed solution requires multiple changesto the existing communication network.

[0016] Document WO-A-00/21319 discloses the identification of a mobilestation in a packet radio network. In this connection, the prior artdocument discloses that a temporary identity allocated to a mobilestation by a core network element is allocated such that the networkelement encodes its own identifier, or part of it, into the temporaryidentity. The identity of the network element such as a SGSN node isassumed in this prior art to be derivable on the basis of the identitiesof the routing area served by the network element. However, as explainedabove, this assumption is no longer valid as a respective routing areais handled by several (different) network elements of the same networkelement type but of different core network types.

[0017] Therefore, the teaching as presented in WO-A-00/21319 can not betransferred to the present scenario in which it is required that arespective routing area has to be connectable to different core networkelements of the same type.

SUMMARY OF THE INVENTION

[0018] Hence, it is an object of the present invention to provide animproved method of performing a routing area update for a terminalequipment in a communication network, which is suitable for a scenarioin which it is required that a respective routing area has to beconnectable to different core network elements of the same type, whilestill keeping the amount of resulting changes small.

[0019] According to the present invention, this object is for exampleachieved by a method of performing an area update for a terminalequipment in a communication network, the communication networkcomprising at least two areas being defined within an access network, atleast one of said areas being served by at least two core networkelements of corresponding network element types, each of said at leasttwo core network elements communicating with said access networkdefining said areas via a different interface, the method comprising thesteps of: monitoring, at the terminal equipment side, via which of saidat least two core network elements serving a currently visited area thecommunication with the terminal equipment is effected, detecting, at theterminal equipment side, an area update condition for said terminal,requesting, by said terminal equipment, an area update for said terminalequipment, and wherein said terminal equipment sets an identifier insaid area update request identifying the core network element via whichthe communication with the terminal equipment has previously beeneffected.

[0020] According to further developments of the present invention,

[0021] said identifier set by said terminal equipment is part of therouting area identifier RAI;

[0022] said routing area identifier RAI is composed of a mobile countrycode MCC, a mobile network code MNC, a location area code LAC, and arouting area code RAC;

[0023] said identifier is at least one predetermined bit within saidrouting area identifier;

[0024] said identifier is the most significant bit of said routing areacode RAC;

[0025] said identifier is the most significant bit of said location areacode LAC;

[0026] a setting state of said most significant bit indicates arespective interface via which the previous routing and/or location areaupdate has been performed such that said access network is connected toone of said different core networks;

[0027] for 2^(N) core network elements of a same network element type,the number of predetermined bits is predetermined to be N,

[0028] said identifier set by said terminal equipment is part of thelocation area identifier (LAI).

[0029] Stated in other words, the core network element via which thecommunication with the terminal equipment has previously been effectedis identified with the aid of the type of access network interfacebetween the access network and the core network element.

[0030] Also, the object of the present invention is for example achievedby a terminal equipment adapted to communicate via an access networkwith different core networks and adapted to carry out the method asdefined herein above.

[0031] Accordingly, with the present invention it is advantageouslyenabled that the above mentioned problem is solved.

[0032] Also, no changes to the radio access network are required and there-allocation of the routing area identifier, more precisely, there-allocation of the routing area code within the routing areaidentifier, does not require any procedural changes to existingsignaling. Re-allocation of the routing area identifier here means thatonly part (some bits) of the routing area identifier is used for routingarea identification while another part of it is used for identificationof the core network type to which the access network is connected forcommunication with the terminal equipment. Stated in other words, theRAI is partitioned to be used in parallel for routing area and corenetwork identification.

[0033] Furthermore, as the identifier is carried as a part of the RAIthis enables that no modifications are required to previously existing(“old”) core network elements.

[0034] Rather, it is merely required to adapt the mapping involved withthe routing area code RAC.

[0035] Still further, due to the terminal equipment performing thesetting of the identifier, the core network is at least relieved fromthis network management function to be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and still other objects, features and advantages of thepresent invention will become more fully apparent upon consideration ofthe accompanying drawings, in which:

[0037]FIG. 1 illustrates a basic scenario of routing areas eachconnected to two core network elements of a same type but of respectivedifferent core networks, and a routing area update signaling involved inrouting area update.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will now be explained in detail withreference to the drawings.

[0039]FIG. 1 illustrates a basic scenario of routing areas eachconnected to two core network elements of a same type but of respectivedifferent core networks, and a routing area update signaling involved inrouting area update.

[0040] Nevertheless, it has to be noted that the cells of the newrouting area do not necessarily have to be connected to two core networkelements of a same type but of respective different core networks,rather it is sufficient for the present invention if at least one, i.e.only the previously visited, routing area to which registration has beenperformed is connected to two core network elements of a same type butof respective different core networks. Firstly, the basic scenario willstatically be described, i.e. without a focus to any signaling messagesexchanged between the network elements.

[0041]FIG. 1 illustrates two routing areas 5 and 6, respectively.However, more than two routing areas are normally present within acommunication network, but in order to keep the illustration simple forexplanatory purposes, only two are shown. Each routing area 5, 6 isroughly represented as consisting of several individual cells. A cell isintended to be represented by a respective antenna representation as asymbol for a base station (not shown) with corresponding coverage area.Each routing area is identified by a routing area identifier RAI.

[0042] The routing area identifier RAI consists of four individualfields, i.e. MCC (mobile country code), MNC (mobile network code), LAC(location area code), and RAC (routing area code). The MCC identifiesthe country in which the network is operated, the MNC identifies thenetwork (and via the network, the operator thereof). The LAC identifiesthe location are (i.e. cell or cell group). MCC, MNC, and LAC, however,of routing areas 5 and 6, respectively, are not shown in the FIG. 1.Rather, FIG. 1 indicates only the value of the routing area code RAC forthese routing areas (RAC1 and RAC2). The RAC is an octet of eight bitlength, and its value is indicated in hexadecimal notation. Namely,RAC1=70 “H”=0111 0000 “B” in binary representation. Likewise, routingarea 6 is identified by routing area code RAC2=71 “H”=0111 0001 “B”.

[0043] Each routing area 5, 6 represents an access network of a type, towhich at least two types of core networks are connectable. For thepresent invention, a GERAN cell/routing area has been chosen as anexample. However, the present invention is not limited to GERAN.

[0044] Thus, to the routing area 5 there is connected

[0045] 1) a 2G core network for packetized data transmission representedby a core network element of a type of a 2G SGSN denoted by numeral 2,connected via an interface Gb, and

[0046] 2) a 3G core network for packetized data transmission representedby a core network element 3G SGSN denoted by numeral 1, connected via aninterface Iu-PS (Iu interface for packet switched traffic).

[0047] Likewise, to the routing area 6 there is connected

[0048] 1) a 2G core network for packetized data transmission representedby a core network element of a type of a 2G SGSN denoted by numeral 2(the identity of the 2G core network elements is for simplification ofthe explanation and drawing only, it is of course possible thatdifferent core network elements of the same functionality of the 2G corenetwork are connected to different routing areas without any change inthe present invention), connected via an interface Gb, and

[0049] 2) a 3G core network for packetized data transmission representedby a core network element 3G SGSN denoted by numeral 3, connected via aninterface Iu-PS (Iu interface for packet switched traffic).

[0050] As already mentioned before, it is also possible that the routingarea 6 (to which the terminal equipment moves from the old/previousrouting area) is connected only to a single core network element, whilethe present invention would still remain applicable to such a scenario.

[0051] A terminal equipment such as a mobile station MS or userequipment UE denoted by reference sign 4A, 4B representative ofrespective different situations for the terminal is communicatingvia/with the network and its network elements. Any terminal equipmentmay be used (radio or non-radio) as long as it is adapted forcommunication with different core networks. Also, any access network maybe used, i.e. radio access network or non-radio access network, as longas it is adapted to the used terminal equipment.

[0052] The terminal equipment, in a first situation, is denoted by 4Aand is attached to the “left hand” routing area identified by RAC1=“70Hex”. The terminal equipment has a knowledge of the routing areaidentifier as the identifier is broadcasted by the access network suchas GERAN. Namely, at the terminal equipment side, it is monitored viawhich of said at least two core network elements serving the currentlyvisited routing area 5 the communication with the terminal equipment 4Ais effected.

[0053] As the terminal in the illustrated example is a mobile terminal,it moves during communication as indicated by the dotted arrow. Themoving of the terminal equipment results in the terminal equipmentleaving the previous routing area 5 and entering a new routing area 6.Thus, upon entering the new routing area the terminal equipment detectsthis condition resulting in the necessity for a routing area update tobe performed.

[0054] For explanatory purposes only, it is now assumed that the routingarea update request issued by the terminal equipment is forwarded to thecore network element denoted by numeral 3 of the 3G core network, i.e.to the 3G SGSN connected to the routing area 6.

[0055] Based on the result of monitoring, the terminal 4B in thissituation knows the type of access network interface (Iu or Gb) betweenthe radio network and the core network element via which thecommunication with the terminal equipment 4B (in situation 4A) haspreviously been effected. Thus, dependent on the result, the terminalequipment is adapted to forward two different RAU requests to the “new”core network element, i.e. 3G SGSN denoted with 3.

[0056] In a first case, it is assumed that in the routing area 5 whichhas previously been left by the terminal equipment, the connection hasbeen established via the Gb interface to the 2G SGSN denoted by 2. Inthe routing area update request denoted by 7 a, the terminal equipmentincludes the information on the old and/or previous routing area code(unchanged) so that an information of an RAI with an RAC=70 “Hex” isincluded in the request. Based on the information in the mostsignificant bit MSB of the RAC=0111 0000 “B”, i.e. “0”, the core networkelement 3 receiving the routing area update request knows the type ofthe interface via which the (“previous”) communication in the previousrouting area was effected. The interface type is again representative ofthe core network type (e.g. 2^(nd) or 3^(rd) generation). Then, as the3G SGSN denoted with 3 knows that in the previous routing area 5 thecommunication was effected via the interface Gb, it addresses the 2GSGSN core network element denoted by 2 in order to obtain the subscriberinformation associated to the terminal equipment 4A, 4B requesting therouting area update. This exchange of information between the 2G SGSNdenoted by 2 and the 3G SGSN denoted by 3 is indicated by the arrow 7 b.

[0057] If, on the other hand, it is assumed that in the routing area 5which has previously been left by the terminal equipment, the connectionhas been established via the Iu-PS interface to the 3G SGSN denoted by1, then in the routing area update request denoted by 8 a, the terminalequipment includes the information on the old and/or previous routingarea code with a modified most significant bit so that an information ofan RAI with an RAC=F0 “Hex” is included in the request. Based on theinformation in the most significant bit MSB of the RAC=1111 0000 “B”,i.e. “1”, the core network element 3 receiving the routing area updaterequest knows the type of the interface via which the previouscommunication in the previous routing area was effected. The interfacetype is again representative of the core network type (e.g. 2^(nd) or3^(rd) generation). Then, as the 3G SGSN denoted with 3 knows that inthe previous routing area 5 the communication was effected via theinterface Iu-PS, it addresses the 3G SGSN core network element denotedby 1 in order to obtain the subscriber information associated to theterminal equipment 4A, 4B requesting the routing area update. Thisexchange of information between the 2G SGSN denoted by 2 and the 3G SGSNdenoted by 3 is indicated by the arrow 8 b.

[0058] A similar signaling (not shown) takes place in case of therouting area update request being forwarded to the core network element2 (i.e. 2G SGSN). If in the previous routing area, communication waseffected via the Gb interface, the 2G SGSN 2 learns that it does nothave to contact any other core network element as in the illustratedexample it itself has been in charge for communication with the terminalequipment. If on the other hand in the previous routing area,communication was effected via the Iu-PS interface, the 2G SGSN 2 learnsthat it has to contact the core network element 3G SGSN denoted by 1, sothat a corresponding subscriber data exchange would be effected between3G SGSN denoted by 1 and 2G SGSN denoted by 2.

[0059] Thus, each routing area has a single RAI containing a LAC andRAC. The terminal equipment indicates in the registration to a new corenetwork element upon routing area update the mode (i.e. the type ofinterface, Iu versus Gb) in which a previous registration has beeneffected to a core network element in a previous routing area.

[0060] The invention proposes to re-allocate the RAC space by shorteningthe RAC space from eight to seven bits. Then, the most significant bitin the RAC indicates the type of the interface via which communicationin the previous routing area was effected.

[0061] Also, in case there is an access network which is simultaneouslyadapted for circuit switched data transmission, in FIG. 1 also aninterface Iu-CS to a 3G MSC/VLR (not shown) and an A-interface to a 2GMSC/VLR (not shown) would be present. In such a case, the mostsignificant bit of the LAC within the RAI is proposed to be used forindicating the type of interface via which communication in the previousrouting area was effected. This would result in shortening the LAC from16 to 15 bits. A corresponding signaling in connection with routing areaupdate will in this case be similar to the one as explained above.

[0062] According to a conceivable modification, also the LAC only couldbe used in case of a routing area updating. This alternative has theadvantage that the RAC would not have to be shortened, since it isalready only 8 bits long. I.e. according to the modification the mostsignificant bit of LAC in RAI indicates the previous type of interfaceused. This alternative could be applicable if only routing areas can beconnected to two core network nodes, but location areas are alwaysconnected to only one core network node.

[0063] Still further, herein above an explanation has been given forcases in which there is provided an access network to which two types ofcore networks are connectable. Nevertheless, the present inventionremains still applicable in a case in which 2^(N) types of core networks(with a corresponding number of 2^(N) core network elements of a samenetwork element type) are connectable to the access network (routingarea). In such a case, the invention is easily to be adapted byselecting N as the number of predetermined bits, by which the LAC and/orRAC is to be shortened.

[0064] Thus, as has been explained above in connection with the presentinvention, the present invention solves a previously non-existingproblem as only one core network element of a type (e.g. SGSN) perrouting area RA was possible. Among others, the idea of the inventionresides in using e.g. the most significant bit of the routing area codeRAC of the “old”, i.e. previous routing area RA to indicate to the newnetwork element such as a SGSN the type of the old SGSN. Otherwise, theold routing area code RAC is carried in the GPRS routing area updatemessage to the new SGSN normally, that is unchanged. By inspecting thebit in the routing are identifier RAI and/or routing area code RACand/or location area code LAC, the network element such as the SGSNknows which and which kind of network element (e.g. SGSN) to contact. Inother words, in the network elements such as SGSN's, there will be twomappings for a masked routing area code RAC. One for most significantbit value 1 and one for value 0. The mappings correspond to thedifferent core network systems.

[0065] It should be noted that although the preceding descriptionreferred to routing areas as an example, the present invention isapplicable to other types of areas in communication networks such aslocation areas or simply cells as a minimal area. In addition, althoughthe description focused on plural core network elements of same networkelement type being connected to an area (e.g. SGSN's), the invention isnot limited thereto. Rather, the invention is also applicable to casesin which only plural core network elements of corresponding networkelement types are connected to an area. This means that the core networkelements merely have to be provided with roughly corresponding functionsto be performed, that is, for example, the core network elementsconnected to an area need only to have a common subset of functions ofthe overall functions which they are adapted to perform. Still further,the above description focused on a case in which the core networkelements were assumed to be belonging to different core networks (secondgeneration 2G and third generation 3G). Nevertheless, this is notrequired for the present invention and the core network elements couldactually be in the same common network (e.g. an operator's IP subnet),as long as the access network interface types via which these areconnected (such as Iu-PS and Gb) are different.

[0066] The correspondence of the network element types stated in abovecan be interpreted differently in different embodiments. In someembodiments of the invention the two core network element types servingthe area are of rather similar type, for instance a 2G-SGSN and a3G-SGSN. In other embodiments of the invention, the two types of corenetwork elements may have different functionalities with respect to, forinstance, user plane routing. It can be envisioned, for instance, thatone type of the corresponding network element types is only performingmobility management related functions, whereas the rest of the functionsare performed by other network elements. However, an another type of thecorresponding network element types would also perform additionally manyother functions such as participating in the routing of user planetraffic. However, they have at least one corresponding functionprovided, therefore they are only of corresponding types, not similarwith respect to the set of functions provided. By corresponding type ismeant that the two types of core network elements are both equippedwith, as already mentioned, at least the means of communicating with theaccess network.

[0067] Accordingly, as has been described herein before, the presentinvention proposes a method of performing an area update for a terminalequipment 4A, 4B in a communication network 1, 2, 3, 5, 6, thecommunication network comprising

1. A method of performing an area update for a terminal equipment (4A,4B) in a communication network (1, 2, 3, 5, 6), the communicationnetwork comprising at least two areas (5, 6) being defined within anaccess network, at least one of said areas being served by at least twocore network elements (1-2, 2-3) of corresponding network element types,each of said at least two core network elements communicating with saidaccess network defining said areas via a different interface (Iu, Gb),the method comprising the steps of: monitoring, at the terminalequipment side, via which of said at least two core network elements (1,2) serving a currently visited area (5) the communication with theterminal equipment (4A) is effected, detecting, at the terminalequipment side, an area update condition for said terminal (4A, 4B),requesting, by said terminal equipment, an area update for said terminalequipment (4B), and wherein said terminal equipment (4B) sets anidentifier in said area update request identifying the core networkelement via which the communication with the terminal equipment (4A) haspreviously been effected.
 2. A method according to claim 1, wherein saididentifier set by said terminal equipment is part of the routing areaidentifier (RAI).
 3. A method according to claim 2, wherein said routingarea identifier (RAI) is composed of a mobile country code (MCC), amobile network code (MNC), a location area code (LAC), and a routingarea code (RAC).
 4. A method according to claim 3, wherein saididentifier is at least one predetermined bit within said routing areaidentifier.
 5. A method according to claim 4, wherein said identifier isthe most significant bit of said routing area code (RAC).
 6. A methodaccording to claim 4, wherein said identifier is the most significantbit of said location area code (LAC).
 7. A method according to claim 5or 6, wherein a setting state of said most significant bit indicates arespective interface via which the previous routing and/or location areaupdate has been performed such that said access network is connected toone of said different core networks.
 8. A method according to claim 4,wherein for 2^(N) core network elements of a same network element type,the number of predetermined bits is predetermined to be N.
 9. A methodaccording to claim 1, wherein said identifier set by said terminalequipment is part of the location area identifier (LAI).
 10. A terminalequipment adapted to communicate via an access network with differentcore networks and adapted to carry out the method as defined in any ofthe preceding claims 1 to 9.